Image from Wikipedia - https://en.wikipedia.org/wiki/Gulf_of_Mexico#/media/File:Mississippiriver-new-01.png
Using the 3,000 stream gauges, 50+ nitrate sensors, and 31 monitoring sites the USGS operates, NOAA and its partners predict the 2019 dead zone in the Gulf of Mexico to be about 7,829 sq km which is almost the size of Massachusetts!
The 2018 dead zone was 5,780 sq miles , just slightly over the 5 year average size of 5,770 square miles. While this year’s predicted zone is significantly larger than the average, it is still less than the record size of 8,776 sq mi.
What causes dead zones?
Farms and agricultural areas use phosphorous and nitrate as fertilizers for their fields. When it rains, the excess is carried into the nearest body of water as runoff. Eventually the water makes it downstream, taking with it all the run off. In this case, once the waters of the Mississippi River reach the Gulf of Mexico, the excess nutrients act as a food sources causing an overgrowth of algae. Over a short period of time, the algae die off, leaving low oxygenated waters in their wake. Surface waters will still have some mixing, but the deeper water ends up lacking the oxygen that marine organisms to survive, thus creating mass die off events. Think back 2 years ago when the media was inundated with devastating images of shorelines covered in dead fish.
Why is 2019 special?
There has been a LOT of rain this year, especially in the Mississippi River watershed which empties directly into the Gulf of Mexico. Lets look at how this year stacks up to previous averages. The following are how this year compares to the past 38 years.
2019 Mississippi and Atchafalaya River Discharge……………………………………………………^ 67%
2019 Nitrate Discharge………………………………………………………..156,000 metric tons……..^ 18%
2019 Phosphate Discharge……………………………………………….25,300 metric tons…….….^ 49%
All the rainfall that took place this spring had a big impact on the predicted dead zone size, but other factors like tropical storms or hurricanes could also impact the dead zone as the large systems can mix up the water. This is why NOAA will wait to confirm the official size of the dead zone until August.
What do you think should be done to help prevent these large hypoxic events in the Gulf of Mexico?
Want some more details? Feel free to check out the article here or look at some of NOAA’s flood inundation maps.